There are systems known to the prior art which function to apply a vacuum to a container before filling the container with powdered metal and which seal the container before the container is removed from the assembly to prevent the ingress of gases into the cavity filled with the powdered metal. In accordance with the prior art procedures, a thick-walled container having a cavity therein and of the type disclosed and claimed in U.S. Pat. No. 4,142,888 in the name of the inventor named herein and assigned to the assignee of the subject invention is filled with powder through a fill passageway while under a vacuum. The filling and sealing of the container, while under a vacuum, may be conducted in accordance with the techniques of co-pending application Ser. No. 364,789 filed Apr. 2, 1982 in the name of Wendell E. Parker and assigned to the assignee of the subject application wherein a spherical ball is inserted or forced into the fill passageway after the cavity in the container has been filled with powdered metal while remaining under a vacuum environment. Thereafter, the container, with the ball seal in place, is removed from the filling apparatus and heated and placed in a press for compaction and densification of the powder within the cavity of the container. In many instances, the ball seal is of a different material than the container and, therefore, has a different coefficient of thermal expansion so that upon heating of the assembly prior to compaction, there may result leakage between the ball and the container because of the difference in thermal expansion. Thus, the ball seal may provide a very effective seal at the temperatures utilized for filling the container but may leak at higher temperatures to which the container is subjected.